Control of exhaust flow in an engine including a particulate filter

ABSTRACT

Methods and systems for controlling operation of exhaust of an engine including a particulate filter are provided. One example method includes generating vacuum during engine operation, and storing the vacuum. The method further includes, during or after engine shutdown, drawing ambient air through the particulate filter via the vacuum.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/246,944, entitled “PARTICULATE FILTER REGENERATION DURINGENGINE SHUTDOWN,” filed Sep. 29, 2009, the disclosure of which is herebyincorporated by reference in its entirety and for all purposes.

TECHNICAL FIELD

The present application relates generally to an engine having an exhaustsystem which includes a particulate filter.

BACKGROUND AND SUMMARY

Direct injection (DI) engines may produce more soot than port fuelinjected engines in part due to diffuse flame propagation. As aconsequence of diffuse flame propagation, fuel may not adequately mixwith air prior to combustion, resulting in pockets of rich combustionthat generate soot. Further, DI engines may be susceptible to generatingsoot during high load and/or high speed conditions when there is a lackof sufficient air and fuel mixing.

The inventors herein have recognized various issues in applyingparticulate filters to DI, spark-ignition engines. For example, it canbe difficult to maintain accurate emission control during particulatefilter regeneration in a DI, spark-ignition engine.

Thus, methods and systems for controlling operation of exhaust of anengine including a particulate filter are described herein. Oneexemplary method includes generating a vacuum during engine operationand storing the generated vacuum. Ambient air can be drawn through theparticulate filter via the vacuum during and/or after engine shutdown toat least partially regenerate the particulate filter.

By performing the regeneration during and/or after engine shutdown, theparticulate filter can be regenerated by an increased flow of oxygen tothe particulate filter while avoiding potential increased emissions froma three-way catalyst in an exhaust tailpipe.

In one example, the vacuum may draw fresh air in a reverse directionthrough the filter. By controlling the system to draw fresh air into theparticulate filter in a direction that is the reverse of a direction ofexhaust flow during engine combustion, improved removal of soot may beachieved.

Yet another potential advantage of regenerating the filter during and/orafter engine shutdown using stored vacuum is that a regenerationreaction can be delayed or advanced to a time when particulate filterconditions are appropriate for carrying out the regeneration reaction.For example, the stored vacuum may be stored until the particulatefilter temperature becomes hot enough to carry out the regenerationreaction due to natural temperature increases that can occur after anengine shutdown. Further still, particulate filter regeneration may beselectively carried out under particular engine shutdown conditions(e.g., shutdowns in which filter regeneration is already commencedduring engine running conditions, or shutdowns in which filtertemperature is high enough), and not during others.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine with a turbocharger and anexhaust gas recirculation system.

FIG. 2 shows a flowchart illustrating a method for managing particulatefilter regeneration in a direct injection gasoline engine in a vehicle.

FIG. 3 shows a flowchart illustrating a method for storing vacuum duringengine shutdown.

FIG. 4 shows a flowchart illustrating a method for regenerating aparticulate filter during engine shutdown, using stored vacuum.

FIG. 5 shows a flowchart illustrating a method for starting an enginebased on filter regeneration carried out during and/or after a previousengine shutdown.

DETAILED DESCRIPTION

The following description relates to a method for regenerating aparticulate filter in an engine, such as a direct injection gasolineengine. During a first operating condition of the engine, combustion inthe engine may be carried out about stoichiometry and exhaust gas mayflow from the engine in a first direction, to a particulate filter wheresoot generated by the engine is collected. During engine operation,vacuum generated by engine spinning (or pressure generated byturbocharger motion) may be stored in the intake system, such as in theintake manifold. Then during a subsequent engine shutdown (e.g., duringengine spin-down after combustion has stopped, or during engine rest),the stored vacuum or pressure may be applied to generate regenerationflow to the filter. For example, stored vacuum may be used to draw freshair into the filter from ambient atmosphere (e.g., via the tailpipeand/or engine inlet) in a second, reverse direction, to aid in filterregeneration. Alternatively, stored pressure may be used to push freshair from the intake manifold to the filter to aid in filter regeneration

In some embodiments, one or more exhaust gas recirculation (EGR) systemsmay be utilized to allow the fresh ambient air to flow from the filterto the stored vacuum. For example, when a vacuum is created in an intakemanifold, fresh air may flow into the intake system, through a lowpressure EGR system toward the particulate filter, then back through ahigh pressure EGR system to an area of low pressure (e.g., vacuum)stored in the intake manifold. In other embodiments, fresh air may bedrawn in through the tailpipe, through the particulate filter, and thenthrough an EGR system (e.g., a high pressure EGR system) to low pressurein the intake manifold, or elsewhere in the intake system. Still othervariations may also be used.

Turning now to FIG. 1, a schematic diagram shows one cylinder ofmulti-cylinder engine 10, which may be included in a propulsion systemof an automobile. Engine 10 may be controlled at least partially by acontrol system including controller 12 and by input from a vehicleoperator 132 via an input device 130. In this example, input device 130includes an accelerator pedal and a pedal position sensor 134 forgenerating a proportional pedal position signal PP. Combustion chamber(i.e., cylinder) 30 of engine 10 may include combustion chamber walls 32with piston 36 positioned therein. In some embodiments, the face ofpiston 36 inside cylinder 30 may have a bowl. Piston 36 may be coupledto crankshaft 40 so that reciprocating motion of the piston istranslated into rotational motion of the crankshaft. Crankshaft 40 maybe coupled to at least one drive wheel of a vehicle via an intermediatetransmission system. Further, a starter motor may be coupled tocrankshaft 40 via a flywheel to enable a starting operation of engine10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

Intake valve 52 may be controlled by controller 12 via electric valveactuator (EVA) 51. Similarly, exhaust valve 54 may be controlled bycontroller 12 via EVA 53. Alternatively, the variable valve actuator maybe electro hydraulic or any other conceivable mechanism to enable valveactuation. During some conditions, controller 12 may vary the signalsprovided to actuators 51 and 53 to control the opening and closing ofthe respective intake and exhaust valves. The position of intake valve52 and exhaust valve 54 may be determined by valve position sensors 55and 57, respectively. In alternative embodiments, one or more of theintake and exhaust valves may be actuated by one or more cams, and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems to vary valve operation. For example, cylinder 30 mayalternatively include an intake valve controlled via electric valveactuation and an exhaust valve controlled via cam actuation includingCPS and/or VCT.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion chamber 30. The fuel injector may be mounted in theside of the combustion chamber or in the top of the combustion chamber,for example. Fuel may be delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

Intake passage 42 may include throttles 62 and 63 having throttle plates64 and 65, respectively. In this particular example, the positions ofthrottle plates 64 and 65 may be varied by controller 12 via signalsprovided to an electric motor or actuator included with throttles 62 and63, a configuration that is commonly referred to as electronic throttlecontrol (ETC). In this manner, throttles 62 and 63 may be operated tovary the intake air provided to combustion chamber 30 among other enginecylinders, and may also be operated to control a vacuum or pressure inthe intake manifold, as will be discussed. The positions of throttleplates 64 and 65 may be provided to controller 12 by throttle positionsignals TP. Intake passage 42 may include a mass air flow sensor 120 anda manifold air pressure sensor 122 for providing respective signals MAFand MAP to controller 12.

Engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 162arranged along intake manifold 44. For a turbocharger, compressor 162may be at least partially driven by a turbine 164 (e.g., via a shaft)arranged along exhaust passage 48. For a supercharger, compressor 162may be at least partially driven by the engine and/or an electricmachine, and may not include a turbine. Thus, the amount of compressionprovided to one or more cylinders of the engine via a turbocharger orsupercharger may be varied by controller 12. Further, turbine 164 mayinclude wastegate 166 to regulate the boost pressure of theturbocharger. Similarly, intake manifold 44 may include valved bypass167 to route air around compressor 162.

As shown, throttle 62 is positioned downstream of compressor 162 anddownstream of the valved bypass 167, and throttle 63 is positionedupstream of both the compressor 162 and the valved bypass 167. Selectivecontrol of these throttles, as positioned, may allow for greater controlof generation and storage of vacuum or increased pressure in a portionof the intake manifold. As will be discussed, the generation of vacuumor increased pressure in said portion of the intake manifold is used forregeneration of the particulate filter.

In the disclosed embodiments, and as illustrated in FIG. 1, an exhaustgas recirculation (EGR) system may route a desired portion of exhaustgas from exhaust passage 48 to intake manifold 44 via high pressure EGR(HP-EGR) passage 140 or low pressure EGR (LP-EGR) passage 150.

An HP-EGR passage 140 may have a first opening upstream of the turbineand particulate filter, such that exhaust gas can be routed fromupstream of the turbine 164 of the turbocharger to a second openingdownstream of the compressor 162 of the turbocharger and the throttle 62during engine combustion. The LP-EGR passage 150 may have a firstopening downstream of the turbine 164 and downstream of device 72 (e.g.,particulate filter) such that exhaust gas can be routed from downstreamof the particulate filter 72 to a second opening upstream of thecompressor 162 yet downstream of throttle 63, during engine combustion.In some embodiments, engine 10 may include only an HP-EGR system or onlyan LP-EGR system.

An amount of EGR flow may be varied by selective control of HP-EGR valve142 or LP-EGR valve 152 during engine combustion operation. Further, anEGR sensor, such as HP-EGR sensor 144, may be arranged within either orboth of the HP-EGR and LP-EGR passages and may provide an indication ofone or more of pressure, temperature, and concentration of the exhaustgas therein. Alternatively, the HP-EGR valve and/or LP-EGR valve may becontrolled through a calculated value based on signals from the MAFsensor (upstream of throttle 63), MAP (intake manifold), MAT (manifoldgas temperature) and the crank speed sensor. Further still, flow througheither or both of the HP-EGR and LP-EGR passages may be controlled basedon an exhaust O₂ sensor and/or an intake oxygen sensor (e.g., in anintake manifold). Under some conditions, an EGR system may be used toregulate the temperature of the air and fuel mixture within thecombustion chamber.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control system 70. Further, sensor 127 is shown coupled toexhaust passage 48 upstream of particulate filter 72 and sensor 128 isshown coupled to exhaust passage 48 downstream of particulate filter 72.Sensors 126, 127, and 128 may be a combination of any suitable sensorsfor providing an indication of exhaust gas air/fuel ratio such as alinear oxygen sensor or UEGO (universal or wide-range exhaust gasoxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx,HC, or CO sensor.

Emission control devices 71 and 72 are shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 71 and device 72may include a selective catalytic reduction (SCR) system, three waycatalyst (TWC), NO trap, various other emission control devices, orcombinations thereof. For example, device 71 may be a TWC and device 72may be a particulate filter (PF). In some embodiments, where device 72is a particulate filter, device 72 may be located downstream of device71 (as shown in FIG. 1). In other embodiments, device 72 may be aparticulate filter positioned upstream of device 71, which may be a TWC(this configuration not shown in FIG. 1). Further, in some embodiments,during operation of engine 10, emission control devices 71 and 72 may beperiodically reset by operating at least one cylinder of the enginewithin a particular air/fuel ratio. In still further embodiments, device72 (e.g., particulate filter) may be regenerated while the engine isshut down (e.g. not combusting), as will be described in detail below.Additionally, a tailpipe valve 199 is shown downstream of device 72 inexhaust tailpipe 198. The tailpipe valve 199 may be controlled bycontroller 12, in order to control pressure in the exhaust. This will bediscussed in detail below.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor 102, input/output ports 104, an electronic storage mediumfor executable programs and calibration values shown as read only memory106 in this particular example, random access memory 108, keep alivememory 110, and a data bus. Controller 12 may receive various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; a profileignition pickup signal (PIP) from Hall effect sensor 118 (or other type)coupled to crankshaft 40; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal, MAP, from sensor122. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold. Note that various combinations of the above sensors maybe used, such as a MAF sensor without a MAP sensor, or vice versa.During stoichiometric operation, the MAP sensor can give an indicationof engine torque. Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, may produce a predetermined number of equallyspaced pulses every revolution of the crankshaft.

Storage medium read only memory 106 can be programmed with computerreadable data representing instructions executable by microprocessor 102for performing the methods described below as well as other variantsthat are anticipated but not specifically listed.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine, and that each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

Example control routines for an engine, such as engine 10 describedabove with reference to FIG. 1 are shown and described with respect toFIGS. 2-5. FIG. 2 is a flowchart illustrating a method for managingparticulate filter regeneration in a direct injection gasoline. FIG. 3illustrates example engine shutdown control for storing vacuum. FIG. 4is a flowchart illustrating control of an engine shutdown, or enginerest, regeneration using stored vacuum, and FIG. 5 is a flowchartillustrating an example routine for starting an engine that takes intoaccount whether, and to what extent and/or duration, engine shutdownfilter regeneration was carried out before said starting of the engine.

Turning now to FIG. 2, an operational flow chart illustrating a method200 for managing regeneration of a particulate filter downstream of anengine, such as engine 10 shown in FIG. 1, is shown. Specifically,method 200 demonstrates example operation for managing particulatefilter regeneration of a direct injection gasoline engine, based onengine operating conditions. The method 200 determines whether engineshutdown regeneration is requested, and also determines a timing for anengine shutdown regeneration.

At 210 of method 200, the method includes determining whether the engineis running. This may include determining whether the engine is spinningand carrying out combustion of one or more cylinders. In one example,combustion may include oscillation of the engine air-fuel ratio aboutstoichiometry, where exhaust gas flows from the engine, through aturbine (e.g., turbine 164), and then through a three-way catalyst(e.g., device 71) and a particulate filter (e.g., device 72) beforeexiting through a tailpipe (e.g., exhaust tailpipe 198). If the engineis not running, the method 200 may end. If the engine is running, themethod 200 may proceed to 212.

At 212, an amount of particulate (e.g., soot) in the particulate filteris estimated. In some embodiments, this may include estimating an amountof soot in the particulate filter based on a pressure drop across theparticulate filter. In other embodiments, a soot accumulation model maybe utilized to estimate the amount of soot in the particulate filter.Once the amount of soot is determined, the method continues to 214 todetermine if the amount of soot is greater than a threshold amount(e.g., a first, lower threshold A) which may be used as an indication ofwhether or not to regenerate the particulate filter during and/or afteran engine shutdown.

If the estimated amount of soot is less than the threshold A, asdetermined at 214, the method 200 may continue to 228 where anon-regeneration engine shutdown is requested (e.g., where, if theengine is shut down, the particulate filter is not regenerated duringengine shutdown and/or during engine rest). For example, the method 200may include setting a flag indicating that a request fornon-regeneration engine shutdown has been established. On the otherhand, if the estimated amount of soot exceeds the threshold A, themethod 200 may proceed to 216 to request an engine shutdown regeneration(see FIG. 3).

Then, the method 200 may continue to 218 to determine if the amount ofparticulate stored in the particulate filter is greater than a thresholdamount (e.g., a second, higher threshold B), which may be used as anindication of whether or not to regenerate the particulate filter duringengine running, or engine combustion (e.g., before an engine shutdown).If the answer to 218 is yes, the method 200 may continue to 220 torequest an engine running regeneration at 220. Otherwise, the method 200may end.

At 222, the method 200 includes determining whether regenerationconditions have been met. For example, it may be determined whetherexhaust temperature is greater than a threshold (e.g., a minimumregeneration temperature), or other conditions. In this way, aregeneration reaction can be delayed or advanced to a time whenparticulate filter conditions are appropriate for carrying out theregeneration reaction. For example, the stored vacuum or pressure may bestored until the particulate filter temperature becomes hot enough tocarry out the regeneration reaction.

At 224, the routine performs the engine running particulate filterregeneration. In some examples, an engine running particulate filterregeneration may include adjusting engine operation to raise exhaust gastemperature sufficiently high to initiate filter regeneration withexcess oxygen. For example, engine speed can be increased, throttlingmay be increased, etc. to increase exhaust gas temperature. Duringengine running regeneration, the excess oxygen directed to theparticulate filter for particulate filter regeneration may be suppliedvia one or more of the EGR systems (e.g., by delivering pressurized airfrom the intake to the exhaust, thus bypassing the engine), via an airpump delivering airflow upstream of the particulate filter anddownstream of the three way catalyst, by operating with lean combustionin the engine, or combinations thereof. In one example, during theengine running regeneration of 224, excess oxygen flows to and throughthe particulate filter in a direction from the exhaust manifold, orengine output side of the particulate filter to the tailpipe, oratmospheric side of the particulate filter. Various operating parametersmay be adjusted to control the filter regeneration rate, temperature ofthe exhaust and/or particulate filter, etc.

Referring now to FIG. 3, a method 300 illustrating additional details ofengine shutdown control is described. First, at 310, the method 300includes determining whether an engine shutdown request has been made.For example, the engine shutdown request may be generated from anoperator indicating a request to shut down the vehicle (e.g., by aturn-off the vehicle via a key position of the vehicle). The engineshutdown request may also be generated based on vehicle operatingconditions where engine output torque is not needed, for example, duringdeceleration conditions where the requested engine torque is less thanzero, or in response to a driver tip-out. In still another example, theengine shutdown request may be generated from a hybrid-vehiclecontroller if an engine is in a hybrid electric vehicle, where an engineshutdown can be carried out while the vehicle continues to operateand/or travel, driven by a hybrid propulsion system.

When the answer to 310 is yes, the routine continues to 312 to determinewhether engine shutdown regeneration was requested (e.g., at 220 ofmethod 200). If so, the method 300 continues to 316. Otherwise, themethod 300 may continue to 314 to determine if an engine runningregeneration is already in progress at the time of the engine shutdownrequest. In this case, even though an engine shutdown regeneration wasnot specifically requested, in some conditions, it may be beneficial toextend the engine running regeneration through engine shutdown. Forexample, the regeneration may be extended from engine running operation,through engine spin-down, and through at least a portion of engine rest.Thus, if the answer to 314 is yes, the method 300 may also continue to316, at least under selected conditions (e.g., when there is asufficient amount of particulate stored in the filter, greater than aminimum amount C) to warrant extending regeneration through the engineshutdown. In this example, the operations indicated at 316-322 of themethod 300 may be carried out while particulate filter regeneration isalready underway. Otherwise, the method 300 may end.

If the answer to 314 is no, the method 300 may carry out anon-regeneration engine shutdown (not shown). For a non-regenerationengine shutdown, the method 300 may include reducing, or avoiding astoring of increased pressure and/or vacuum during the engine shutdown,and thus does not include drawing in fresh air during engine shutdownoperation to regenerate, or extend regeneration of, the particulatefilter. Accordingly, particulate filter regeneration may be selectivelycarried out under particular engine shutdown conditions (e.g., engineshutdowns in which filter regeneration is already commenced duringengine running conditions) in some cases, and not during others.

At 316, the method 300 includes adjusting engine operation to generateand/or store vacuum in the intake manifold. In order to create vacuum inthe intake manifold, engine boost may be reduced (via adjustment of aturbine wastegate or a valved bypass of a compressor, for example), anda throttle opening may also be reduced during engine shutdown. Thereduction of engine boost and/or throttle opening may be initiatedduring engine spin-down. By reducing a throttle opening to be nearlyclosed, an increased vacuum can be generated in the intake manifold. Inanother example, the HP-EGR valve may also be closed during enginespin-down, in order to create vacuum and/or increase an amount of vacuumin the intake manifold.

Alternately, at 316, the method may include adjusting operation togenerate and/or store compressed intake gasses (e.g., pressure). Thestored pressure may be generated in the intake manifold by increasingengine boost and throttle opening before the engine stops spinning. Inthis way, pressure in the intake manifold, can be generated and stored(e.g., at a sufficiently high rate and/or under selected conditions suchthat the engine may not utilize the pressure). In some cases, thetailpipe valve may be closed during a portion of engine shutdown toincrease intake manifold pressure.

Additional adjustments to further increase stored pressure or storedvacuum (e.g., in the intake manifold) may be carried out, such asadjusting valve timing. Such adjustments may be concurrent withdiscontinuing combustion in one or more (e.g., all) of the enginecylinders. In this way, it is possible to either increase pressure orgenerate vacuum in the intake manifold via the rotating engine duringengine spin-down, even if the engine speed is decelerating. Compressedair and/or a vacuum may be generated and stored either before, or afterdiscontinuation of combustion, and either before or during enginespin-down. Further, while this example illustrates storing pressureand/or vacuum in the intake manifold, pressure and/or vacuum may bestored at other locations in the intake, such as a pressure or vacuumstorage tank coupled to the intake manifold. Further, pressure and/orvacuum can be stored at any location in the air circulation circuits ofan engine, provided there are appropriate valves and controls forcontrolling the generation, storage, and movement of the stored pressureor vacuum.

Next, at 318, the routine maintains vacuum (or increased pressure) inthe intake manifold, for example, by positioning the throttle in asealed closed position in the intake passage. To maintain pressure inthe intake manifold, the throttle may be closed at a maximum air charge,or when a maximum air charge exists in the portion of the intakemanifold that stores the generated pressure. To maintain vacuum in theintake manifold, the throttle may be moved from almost closed to fullyclosed as the engine spins down to rest, such that the throttle is fullyclosed as engine speed drops below a minimum engine speed, such as 50RPM. By sealing the throttle closed and by stopping the engine at aposition such that there is little or no communication between theintake manifold and exhaust manifold through one or more cylinders ofthe engine (e.g., without positive valve overlap of any one cylinder inthe rest position), it may be possible to temporarily store thegenerated vacuum (or compressed intake gasses) even after the enginecomes to rest. The LP-EGR valve, HP-EGR valve, compressor valved bypass,turbine wastegate, and/or tailpipe valve may also be sealed closed inorder to assist in the storage of the generated vacuum, or compressedair.

During the engine shutdown, the method may include adjusting operatingparameters to increase exhaust temperature at 320. For example, if aparticulate filter temperature is less than a threshold temperature,increasing exhaust temperature may include operating the engine with aretarded spark timing to increase exhaust temperature in preparation forshutdown regeneration. This may be carried out for a selected number ofcombustions, including one or more last combustion events beforediscontinuing combustion.

At 322, the method 300 includes carrying out the engine shutdownregeneration. In one example, the method 300 may include temporarilystoring the compressed air or generated vacuum in the intake until apeak particulate filter temperature, or temperature range, is reached,and thereafter dissipating the compressed air or stored vacuum at 322.For example, stored vacuum may be dissipated by opening a tailpipe valveand thus drawing in fresh air, where the fresh air passes through theparticulate filter. Because temperatures may temporarily rise after ashutdown operation, the method 300 may include holding the compressedair or the vacuum until the peak filter temperature, or temperaturerange, is reached, before adjusting one or more valves to use the vacuumor compressed air to increase oxygen flow to the particulate filter, andthus regenerate the particulate filter. In this way, fresh air will bedrawn in to a particulate filter when it is subject to a favorabletemperature for carrying out the regeneration reaction. In anotherexample, the method 300 may include increasing the flow of fresh air atthe particulate filter as the exhaust temperature temporarily increasesduring an engine shutdown.

Additional details of engine shutdown regeneration are described withregard to FIG. 4, for example. Specifically, the method 400 includesdetermining, at 410, whether temperature is greater than a thresholdtemperature value. For example, the method 400 may include determiningif temperature has risen during engine shutdown and/or engine restconditions to above the threshold temperature, or if it was alreadyabove a threshold temperature before the engine shutdown. In this way,it can be further determined whether or not to perform engine shutdownregeneration. For example, particulate filter regeneration may beselectively carried out under particular engine shutdown conditions(e.g., shutdowns in which filter temperature is high enough), and notduring others. The fresh air to the particulate filter may be drawn invia stored vacuum (or pressure) at different times after the engine hasstopped, based on different temperature conditions of the exhaust, forexample. Additional parameters may also be monitored at 410, includingwhether the engine has come to a complete stop, and/or whether storedvacuum level is greater than a threshold level (e.g., whether pressurein the intake manifold is less than a threshold absolute pressure). Inthe example where pressure is stored in the intake manifold, the method400 may also include determining whether manifold pressure is above athreshold absolute pressure (e.g., such that it is sufficiently high topush a desired amount of oxygen to the particulate filter).

When the answer to 410 is yes, the method 400 continues to 412 to adjustone or more EGR system parameters and/or intake or exhaust systemparameters to draw fresh air through the particulate filter via thevacuum in the intake. In other examples, air may be drawn toward theparticulate filter via stored pressure in the intake. The adjusting ofthe flow through the filter may be based on feedback of various sensors,as described herein.

In one example where a vacuum has been generated in the intake manifold,both the HP-EGR and LP-EGR passages may be used during the particulatefilter regeneration, where a compressor bypass is closed (e.g., valvedbypass 167 of FIG. 1 is closed), a turbine wastegate is at leastpartially opened, and the tailpipe valve is closed. In this case, boththe HP and LP-EGR valves (e.g., HP-EGR valve 142 and LP-EGR valve 152 ofFIG. 1) are each at least partially opened to initiate the flow of freshair to the particulate filter. Thus, if a vacuum has been generated inthe intake manifold, fresh air can be drawn in from intake passage(e.g., by opening a throttle), pass through the LP-EGR passage, and flowthrough the particulate filter in a reverse direction. That is, theairflow may travel through the particulate filter in a directionopposite to an exhaust gas flow direction when the engine is running,without removing the filter from the exhaust system, and withoutreconfiguring the position of the particulate filter in the exhaustsystem. From the particulate filter, the fresh airflow travels aroundthe turbine via the turbine wastegate and then through the HP-EGRpassage to the intake manifold.

In another example in which a vacuum has been generated in the intakemanifold, fresh air may be drawn in through the particulate filter byopening a tailpipe valve downstream of the particulate filter (ifequipped), the turbine wastegate, and/or the HP-EGR valve. In this case,the LP-EGR valve may be closed or the LP-EGR passage may be omitted. Thefresh airflow may be drawn in through the tailpipe, pass through theparticulate filter in a reverse direction compared to the direction ofexhaust during engine combustion operation (e.g., from an atmosphericside of the particulate filter to an engine output side of theparticulate filter), past the turbine (e.g., though an at leastpartially opened wastegate, or through the turbine), and then passthrough the HP-EGR passage to enter the intake manifold. This mayeffectively dissipate the stored vacuum. In this case, the method mayfurther include adjusting the amount of fresh airflow through the filterduring engine shutdown conditions and/or the timing of fresh air flow byadjusting the opening of one or more of an HP-EGR valve, an LP-EGRvalve, a turbine wastegate, and a tailpipe valve.

In an example where compressed air has been stored in the intakemanifold, the LP-EGR system may be closed during filter regeneration oromitted, and a tailpipe valve may be left open during filterregeneration or omitted. In one example, upon opening of the turbinewastegate and/or HP-EGR valve, the compressed air flows from the intakemanifold, through the HP-EGR passage to the exhaust, past the turbine(e.g., through an at least partially opened wastegate, or through theturbine), and then through the particulate filter and to the atmosphere,thus flowing through the particulate filter in a first directionconsistent with a direction of exhaust flow during engine combustion.Here, one or more of the HP-EGR valve, turbine wastegate valve, ortailpipe valve may be adjusted to control the timing and amount of freshair flowing past the particulate filter. Note in this example, theairflow during an engine shutdown filter regeneration travels in thesame direction as exhaust flow during engine combustion.

In another example, compressed air may be released by opening a tailpipevalve, compressor valved bypass and/or an LP-EGR valve, and closing anHP-EGR valve, for example, thereby pushing the compressed air from theintake side, past the compressor (e.g., via the compressor valved bypassor through the compressor), through the LP-EGR passage, and through theparticulate filter in the reverse direction (e.g., from an atmosphericside of the particulate filter to an engine output side of theparticulate filter), thus allowing the flow of excess oxygen to bypassthe three-way catalyst.

Combinations of the methods provided herein for flowing excess oxygenthrough the particulate filter may be employed. For example, a firstmethod for flowing compressed air through the particulate filter in areverse direction may be carried out until pressure in the intakemanifold has equalized with pressure in the exhaust passage. Thereafter,a second method for flowing compressed air through the particulatefilter in a first direction (e.g., same direction as exhaust flow duringengine combustion) may be carried out.

As mentioned, the timing and/or amount of fresh airflow flowing past aparticulate filter may be regulated by adjusting one or more of athrottle opening, a compressor valved bypass, a turbine wastegate valve,an HP-EGR valve, and an LP-EGR valve. For example, under highertemperature shutdown conditions, the stored pressure or vacuum may beused at a first, earlier timing following a discontinuation of enginecombustion, to take advantage of a high particulate filter temperature.However, under lower temperature conditions, the stored pressure orvacuum may be used at a second, later timing following thediscontinuation of engine combustion, to enable the fresh airflow topass through the filter in coordination with a natural temperature riseat the particulate filter.

The timing and/or amount of fresh airflow may also be regulated based onan amount of excess oxygen detected at the particulate filter by anoxygen sensor. In the case where compressed air or excess oxygen isbeing pushed through the particulate filter in a direction that is thesame as a direction of exhaust flow during engine combustion (e.g., fromengine output side to atmosphere), a first oxygen sensor upstream of theparticulate filter may provide an excess oxygen measurement upon whichairflow adjustments can be made. Further, this approach may also be usedduring engine running filter regeneration to control an amount of excessoxygen delivered to the filter. Alternatively, in the case where avacuum is being used to draw air in from the atmosphere and past theparticulate filter (e.g., in a reverse direction), a second oxygensensor downstream of the particulate filter may provide an excess oxygenmeasurement upon which airflow adjustments are made.

In some cases, it may be possible to adjust engine operation while anengine is still combusting so that during a subsequent engine shutdown,it is possible to generate fresh airflow past the filter to performparticulate filter regeneration. For example, valve positioning and/orengine combustion parameters may be adjusted during one or more lastcombustions before discontinuing combustion. Furthermore, an engineshutdown regeneration may include a continuation or extension of enginerunning regeneration, or it may solely be an engine shutdownregeneration (e.g., initiated during engine shutdown), at least undersome conditions. Such an engine shutdown may be contrasted with anengine shutdown not having particulate filter regeneration.

Finally, the flowchart of FIG. 5 illustrates a control routine 500 forstarting engine combustion after engine shutdown regeneration of theparticulate filter, without any other starts between the shutdownregeneration and the current engine start. Specifically, routine 500adjusts engine operating parameters during engine start based on a stateand extent of the regeneration during and/or after engine shutdown.

At 510 of routine 500 it is determined if the vehicle is on by checkingif a key is on, in this example. If it is determined that the key is noton, routine 500 may end. In some embodiments, such as when the vehiclehas a hybrid-electric propulsion system, the key may have remained onduring engine shutdown, and thus other parameters may be checked at 510to determine if an engine restart is desired.

On the other hand, if it is determined that the key is on, routine 500proceeds to 512 where it is determined if regeneration was attemptedduring a previous engine shutdown. In some embodiments, an engineshutdown may be performed without regeneration of the particulate filter(e.g., without drawing in fresh air via stored pressure/vacuum). If itis determined that regeneration was not attempted or successfullycompleted during a previous engine shutdown, routine 500 may proceed to522 where the engine is started without adjustments for filterregeneration. This may include starting the engine with a first air-fuelratio profile, idle speed set-point, spark timing profile, etc. In oneexample, an air-fuel ratio of an initial combustion event of the startmay be adjusted to be less lean or more rich, in response to a lessextensive (or lack of) engine shutdown filter regeneration.

However, if it is determined that an engine shutdown regeneration wasattempted and/or successfully completed during a previous engineshutdown, routine 500 may continue to 514 where the state ofregeneration is determined. For example, regeneration may have beenstarted, but then discontinued due to an engine start request. Asanother example, regeneration may have started and been terminatedbefore the regeneration of the particulate filter was completed (e.g.,regeneration was partially completed). In further examples, regenerationmay have been started but only a portion of stored soot may have beenremoved by regeneration. Further still, depending on a temperature ofthe three-way catalyst during a previous engine shutdown regeneration,more or less excess oxygen may have been stored at the three-waycatalyst. As such, a state of a three-way catalyst may also bedetermined at 514.

Once the state of regeneration is determined, routine 500 of FIG. 5proceeds to 518 where the engine is started (e.g., begin enginecombustion). Then routine 500 continues to 520 where engine operatingparameters are adjusted based on the state of regeneration. Engineoperating parameters may include, but are not limited to, air fuelratio, spark timing, idle speed setpoint, etc. For example, if theprevious engine shutdown regeneration was attempted and only partiallycompleted, there may be less O₂ in the three way catalyst than if theregeneration had been more fully carried out. As such, the air fuelratio may be adjusted during the engine start to be more rich (or lesslean) of stoichiometry in order to reduce the excess O₂ in the three-waycatalyst during the engine start. In some cases, engine operatingparameters may be adjusted based on the state of the three-way catalyst.

In another example, the engine may be started in such a way as tocontinue regeneration if it was not completed during engine shutdown,and/or if an engine shutdown regeneration is ongoing. For example, in avehicle with a hybrid-electric propulsion system that carried out anengine shutdown regeneration while the engine was still spinning (e.g.,driven by a motor), the engine may need to be restarted as the vehicleaccelerates, and as such, the engine shutdown regeneration of theparticulate filter may not have completed. As such, the air fuel ratiomay be adjusted to be lean of stoichiometry and the spark timing may beretarded in order to continue to supply the particulate filter with O₂for regeneration. Therefore, based on the state of the regenerationduring engine shutdown, the engine may be started in a manner so as tocontinue the regeneration or reduce the effects of the regeneration oncomponents such as the three way catalyst.

As described above with reference to the figures, a direct-injectiongasoline engine may have a particulate filter coupled to its exhaustsystem to collect soot generated during operating conditions, such aswhen the engine is subject to high speed and/or high load. Further, inorder to maintain engine efficiency, the particulate filter may beregenerated, at least partially and at least under some conditions,while the engine is shut down. Based on operating conditions and thevehicle system, stored vacuum and/or pressure in the intake may be usedto facilitate regeneration of the particulate filter during engineshutdown.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system. It will be appreciated thatthe configurations and routines disclosed herein are exemplary innature, and that these specific embodiments are not to be considered ina limiting sense, because numerous variations are possible. For example,the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4,and other engine types. The subject matter of the present disclosureincludes all novel and nonobvious combinations and subcombinations ofthe various systems and configurations, and other features, functions,and/or properties disclosed herein.

The invention claimed is:
 1. A method for controlling operation ofexhaust of a turbocharged engine including a particulate filter,comprising: generating vacuum in an intake manifold of the engine duringengine operation by reducing engine boost; storing the vacuum in theintake manifold; during or after engine shutdown, drawing ambient airthrough the particulate filter via the stored vacuum through an exhaustgas recirculation passage of the engine.
 2. The method of claim 1,wherein drawing ambient air includes drawing the ambient air, by thevacuum, in a reverse flow direction as compared to a direction ofexhaust flow during an engine running operation.
 3. The method of claim1, further comprising: during or after engine shutdown, closing atailpipe valve downstream of the particulate filter in the exhaust flow,where drawing the ambient air includes drawing the ambient air from anintake system, through an LP-EGR system to the particulate filter toregenerate the particulate filter, and through an HP-EGR system to theintake manifold, and regenerating the particulate filter with theambient air drawn to the particulate filter, during engine restconditions.
 4. The method of claim 1, wherein drawing the ambient airincludes drawing the ambient air in from a tailpipe of a vehicle,through the particulate filter, and then through an EGR system to theintake manifold, via the vacuum.
 5. The method of claim 1, furthercomprising adjusting an amount of the ambient air during engine restconditions by adjusting a valve of the engine.
 6. The method of claim 5,further comprising, during or after engine shutdown, adjusting an amountof ambient air to the particulate filter based on an exhaust gas sensor.7. The method of claim 6, wherein adjusting the amount of ambient airincludes adjusting the valve based on a first exhaust gas oxygen sensorlocated between the engine and the particulate filter while ambient airis being drawn through the filter during engine rest conditions, andwhere the method further comprises: during engine running filterregeneration, adjusting flow to the particulate filter based on a secondexhaust gas oxygen sensor located between the particulate filter and atailpipe.
 8. The method of claim 1, further comprising regenerating theparticulate filter during engine running conditions by flowing ambientair through the particulate filter in a first direction, andregenerating the filter after engine shutdown including regenerating theparticulate filter during engine rest by drawing ambient air through theparticulate filter in a second direction opposite to the firstdirection.
 9. The method of claim 1, further comprising continuingregeneration during and after engine shutdown via the vacuum.
 10. Themethod of claim 1, further comprising adjusting an engine operatingparameter during an engine start subsequent to the engine shutdown,based on a particulate filter regeneration during or after the engineshutdown.
 11. The method of claim 10, wherein the engine operatingparameter is an air-fuel ratio of an initial combustion of the enginestart.
 12. A system for controlling operation of exhaust of an engine ina vehicle, the system comprising: an intake manifold upstream of acylinder of the engine; a particulate filter downstream of the cylinder;one or more valves; a turbocharger, an LP-EGR system, and an HP-EGRsystem; and an electronic controller configured to: generate vacuumduring engine operation, store the vacuum in the intake manifold, duringor after an engine shutdown, draw ambient air through the particulatefilter via the stored vacuum; adjust an amount of ambient air drawnthrough the particulate filter by adjusting the one or more valves; andadjust the one or more valves to draw the ambient air in through anintake system, through the LP-EGR system to the particulate filter toregenerate the particulate filter, and through the HP-EGR system to theintake manifold, via the vacuum in the intake manifold.
 13. The systemof claim 12, wherein the one or more valves includes at least one of ahigh pressure EGR valve, a low pressure EGR valve, and a turbochargerwastegate valve.
 14. The system of claim 12, where the electroniccontroller is configured to commence regeneration of the particulatefilter during engine running conditions, and continue the regenerationduring and after engine shutdown via the vacuum.
 15. A method forcontrolling operation of exhaust of an engine including a particulatefilter, comprising: during a first operating condition: generating avacuum during engine operation; storing the vacuum; during or after anengine shutdown from the first operating condition, drawing ambient airthrough the particulate filter via the stored vacuum to at leastpartially regenerate the particulate filter; and during a secondoperating condition: shutting down the engine with less vacuum comparedto the vacuum generated during the first operating condition, whereinthe shutting down is carried out without drawing ambient air through theparticulate filter via the less stored vacuum during engine rest.